The present invention relates to an electrostatic positioner which utilizes electrostatic force to retain a body in a stationary levitation state in a vessel without contact.
In recent intensive research and development of novel materials, it has been proposed to develop novel materials not on the earth but in cosmic space where extremely small gravity is utilized to keep a raw material levitated in a stationary non-contact state at one point in the space for carrying out heating, melting, solidifying or other processes of the material. Realization of such proposal will require development of not only techniques for retaining a body in a stationary non-contact state at one point in the space but also techniques for heating or melting of a retained body.
One of the techniques for retaining a body in a stationary levitation state is to use electrostatic field where any charged body can be retained in a levitation state in the space. In accordance with this concept, practical electrostatic positioners have been proposed.
Such conventional electrostatic positioners are disclosed, for example, in U.S. Pat. No. 4,521,854 and in an article entitled "Development of an electrostatic positioner for space material processing" in REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 56, No. 2, February 1985, pp. 307-317. In a typical example shown in FIG. 1, a pair of dish-like electrodes 1 are vertically spaced apart from each other to produce an electric field therebetween, using a DC power supply 2. In another typical example shown in FIG. 2, four spherical electrodes 3 are disposed at vertexes of a tetrahedron and are respectively connected to their independent DC power supplies 4 to establish an electric field in an inner space of the tetrahedron defined by the electrodes 3. Voltage of the power supply 2 or 4 is controlled such that any deviation in position of the charged body in the electric field defined by the electrodes 1 or 3 is compensated or corrected.
The above-mentioned apparatuses in which the electric field is established by merely applying the direct current to the electrodes 1 or 3 will require monitoring of any deviation in position of the charged body by a video camera or the like as well as control of the power supply 2 or 4 so as to return the body to its stabilized position at a faster response time in response to the monitored result, resulting in technical difficulties in position control of the charged body and in retaining the body in the stationary levitation state.
No confining forces for restricting the body in the lateral directions exist in the electric field established between the disk-like electrodes 1. Such lateral restricting forces are weak even in the electric field established by the spherical electrodes 3. Thus, it arises a problem that the levitated body is liable to laterally escape.
In order to overcome these problems, an apparatus was proposed in which grid-shaped electrodes are used (Japanese Patent Application No. 296782/1988). For instance, as shown in FIG. 3, two pairs of parallel rod-like electrodes 5 are made to intersect in mutually perpendicular relationship, thereby defining a space in the form of a cube. Each electrodes 5 pair is connected to an AC power supply 6 or an AC power supply with direct current component superposed on alternating current.
The electrostatic positioner comprising such even number of rod-shaped electrodes 5 defining a cubic space and connected to the AC power supply 6 has both voltage and frequency controls unlike the apparatuses using the dish-shaped or spherical electrodes 1 or 3, so that it has improved capability for position-controlling of the levitated body. However, the range or zone of effective position control of the levitated body is small so that it remains difficult to maintain the body in the stationary levitation state in a stabilized manner.
The present invention was made to overcome the above and other problems in the conventional apparatuses and has its object to provide an electrostatic positioner having a wide range or zone in which the levitated body can be effectively position-controlled in a stabilized manner.
The present invention will become more apparent from the following description of some preferred embodiments thereof taken in conjunction with the accompanying drawings.